The biology of immature Diptera associated with bacterial decay in the giant saguaro cactus, (Cereus giganteus Engelmann) Item Type text; Thesis-Reproduction (electronic) Authors Santana, Frederick Joseph, 1937- Publisher The University of Arizona. Rights Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. Download date 02/10/2021 16:23:18 Link to Item http://hdl.handle.net/10150/551510 THE BIOLOGY OF IMMATURE DEPTERA ASSOCIATED WITH BACTERIAL DECAY IN THE GIANT SAGUARO CACTUS, (CEREUS GIGANTEPS ENGELMANN). BY Frederick J. Santana A Thesis Submitted to the Faculty of the DEPARTMENT OF ENTOMOLOGY In Partial Fulfillment of the Requirements For the Degree of MASTER OF SCIENCE In the Graduate College THE UNIVERSITY OF ARIZONA 1961 / STATEMENT BY AUTHOR This thesis has been submitted in partial fulfillment of re­ quirements for an advanced degree at The University of Arizona and is deposited in The University Library to be made available to bor­ rowers under rules of the Library. Brief quotations from this thesis are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in their judgment the proposed use of the material is in the interests of scholarship. In all other instances, however, permission must be obtained from the author. SIGNED:. APPROVAL BY THESIS DIRECTOR This thesis has been approved on the date shown below: ACKNOWLEDGMENTS -I wish to express my sincere gratitude to Dr. W. L. Nutting, my major professor under whom this work was done, not only for his constant encouragement, suggestions and criticisms during the research and writing of this paper, but also for an academic association which was of inestimable value. I also wish to thank Dr. F. G. Werner for his helpful criticisms and suggestions concerning the taxonomic section of this study. The general encouragement of Dr. L. A. Carruth and the financial aid made available through him in the form of a graduate assistantship are greatly appreciated. Special thanks also go to Mr. J. 0. Cook, Superintendent of the Saguaro National Monument, for granting approval to use the study area within the Monument. This was of great value since it provided access to a concentrated area of saguaro cacti where the disease was especially prevalent. The following persons are gratefully acknowledged for their help in the determinations of the adult flies: Drs. W. H. Anderson, R. H. Foote, and C. !■/. Sabrosky, all of the D. S. National Museum, Washington, D. C.j Dr. W. B. Heed, Dept, of Zoology, Univ. of Arizona, Tucson; Dr. H. C. Huckett, Riverhead, New York; and Mr. George Steyskal, Grosse lie, Michigan. iii TABLE OF CONTENTS ACKNOWLEDGMENTS.................. ......................... iii INTRODUCTION............................................. 1 MATERIAL AND METHODS.......................................... 5 GLOSSARY...................................................... 9 KEY TO THIRD INSTAR LARVAE................................... 11 KEY TO PUPARIA.......................... 15 DESCRIPTIONS AND BIONOMICS......................... 18 Syrphldae.................................... 18 Otitldae.............. 24 Lonchaeldae........... 27 Neriidae............................................... 31 Milichiidae........................................ 35 Drosophilidae..... ..................................... 42 Sphaeroceridae......................................... 47 Muscidae.................................... 51 SUMMARY....................................................... 55 REFERENCES CITED.............................................. $8 ILLUSTRATIONS iv INTRODUCTION This study has been undertaken to facilitate the identification of the immature, cyclorrhaphous Diptera associated with the bacterial decay of the giant saguaro cactus (Cereus giganteus Engl.)"*" and to provide, in so far as possible, information on the bionomics of each species en­ countered. The saguaro is a characteristic plant of the Sonoran biotic province and, when diseased, it becomes a prime source of food and shelter for dipterous and other insect larvae requiring a semiaquatic to aquatic environment in an area nearly devoid of such habitats. The bacterial necrosis, first reported by Lightle, Standring and Brown (1941), is caused by the bacterium, Erwinia carnegieana Standring. Symptoms of the necrosis follow two patterns according to the above authors, each of which may start in any part of the cactus. The infected region be­ comes water-soaked after bacterial invasion and, with rapid destruction of the internal tissues, the integument breaks down and a brown liquid exudes. Slower, internal decay often occurs, but without the collection of liquid and subsequent bleeding. The term "rot-pocket" was used by Boyle (1949) and is apparently of local origin, referring in a more general way to necrotic lesions that occur at random within the tissues of the cactus. In this study it has been used in reference to any necrotic lesions whether open cavities or small internal infections still covered by the epidermis, Bacterial decay of the saguaro does not always progress in a _________________ Benson, Lyman. 1950. Cacti of Arizona. Tucson: The University Press, pp. 72-76. 1 2 regular manner. By a rapid girdling action the process may cause the loss of a single arm or the toppling of an entire cactus. The disease may be halted temporarily in cacti that fall during the extremely hot and dry months of May, June, and July, because of the high rate of evap­ oration through the broken surfaces. Resumption of rapid decay begins with the following rainy season. Healthy cacti also fall occasionally but mostly during rainy periods which are often accompanied or followed by windstorms. The stages of bacterial necrosis mentioned in this paper are ' . ■ ■ ... characterized by a variety of conditions. The early progress of decay is generally rapid and produces a typical, water-soaked tissue. Cacti often exhibit two different conditions during the later stages of decay. The infected tissue may continue to disintegrate with the aid of numerous dipterous larvae to the final stages of decay or, with fewer larvae present, it may become spongy and eventually dry out. The final stages of decay are characterized by malodorous pools of liquified tissue that remain after the complete breakdown of all tissue and by the darkened, previously infested tissue which never liquified. As mentioned above the necrotic lesions attract numerous insects which either feed on diseased tissues or prey on the saprophytic species present. The spreading of the disease through the surrounding tissues may proceed whether or not diperous larvae, such as Volucella isabellina (Coq.) are present. The author agrees with Boyle (1949) who suspected that dipterous larvae help the spread of the disease by congregating on healthy peripheral tissues, thus preventing corking-off (a natural do- 3 fense mechanism of the cactus). : Existing keys to the larvae of the eyclorrhaphous Diptera are still very incomplete for the most part, while keys to puparia are al­ most non-existent. Specific determinations of immature material must be obtained in the majority of families by rearing and correlating adults with larvae and puparia. Therefore, detailed descriptions and figures of the third larval instars and the pupal stages have been made, and keys provided for identification of the ten species encountered in this study. It is certain that all of the eyclorrhaphous Diptera associated with the giant saguaro have not been found, but the information on the more common species does add to the total knowledge of the immature Diptera and should provide a basis for further work on their role in the bacterial disease of this cactus. In the present paper the use of microscopic characters in the des­ criptions follows a combination of the same general styles used by Nye (1958), Phillips (1946), and Heiss (1938). Characters such as the posterior spiracular slits, ambulatory spicules, and the number of digits on the anterior spiracles provide the most dependable means for making accurate identifications. Of the few previous workers who have studied the insects associated with the saguaro none has ever been concerned with the identification of the immature Diptera. Hubbard (1899), Ryckman and Ames (1953), and Ryckman (i960), in their examination of the cactiphilic insects, were pri­ marily concerned with the adults and presented only faunal lists and biological information about the species studied. As mentioned above, Boyle (1949) briefly discussed the larva of a Volucella sp., but was mainly interested in the pyralid, Gactobrosia fernaldialis. Contribu­ tions by previous workers on the various species encountered in this study will be mentioned under the genera concerned. MATERIAL AND METHODS Larval collections The specimens described in this paper have been collected mainly from the Saguaro National Monument, 15 miles east of Tucson, Arizona, within an area specifically set aside by the National Park Service for research on the giant saguaro cactus. All specimens were collected from standing or fallen cacti in